CN117834127A - CV-MDI-QKD system and method based on DMPM - Google Patents
CV-MDI-QKD system and method based on DMPM Download PDFInfo
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Abstract
The invention discloses a CV-MDI-QKD system and method based on DMPM, and belongs to the technical field of quantum communication. The system comprises n ALICE senders, n BOB senders and n receivers Charlie; the invention encodes the key information to a plurality of discrete and matched specific stages, and then the receiver Charlie publicly announces the homodyne detection result, so that the correlation between the ALICE sender and the BOB sender can be established, RDE is effectively reduced, and the influence of excessive noise of a channel on the key rate is weakened; under the ideal asymmetric condition, the invention can realize safe key distribution under the condition of low-efficiency detection at present, and can reach the quantum limit of discrete coding quantum state discrimination against typical and strong non-Gaussian individual attack; for the symmetric case, the invention can optimize the amplitude and threshold to maximize the key generation rate and the safe transmission distance.
Description
Technical Field
The invention belongs to the technical field of quantum communication, and particularly relates to a CV-MDI-QKD system and method based on DMPM.
Background
Information security is a powerful guarantee for the healthy development of the modern society, and along with the sustainable development of the economy and society, the technology level is continuously advancing, and the requirements of people on communication security are also higher and higher. The security of quantum communication is mainly ensured by the basic principle of quantum mechanics, and the quantum secret communication can realize the secret communication of unconditional security in communication theory by using a 'one-time secret' encryption system.
Quantum key distribution is largely divided into Discrete-variable quantum key distribution (DV-QKD) and Continuous-variable quantum key distribution (CV-QKD); the continuous variable quantum key distribution encodes key information on orthogonal components of a quantum light field, quantum state measurement is carried out by utilizing a homodyne detector, the cost is low, the detection efficiency is high, the continuous variable quantum key distribution can be better fused with the existing optical fiber network, and meanwhile, the continuous variable quantum key distribution has robustness to various noise photons in a quantum channel.
The continuously variable sub-key distribution allows two remote authenticated users (Alice and Bob) to establish a secure key through coherent detection via an untrusted quantum channel and an authenticated classical channel. The key is always encoded by Alice for the orthogonal value and orthogonal selection of the coherent quantized electromagnetic field, and the homodyne detection by Bob can be extracted in cooperation with a post-processing program. The CV-QKD protocol has the inherent characteristics of large transmission capacity, simple hardware realization, effective compatibility with a deployed classical optical communication system and the like. Furthermore, the ideal implementation of CV-QKD can almost approximate the limits of key capacity for unrepeatered quantum communication. Since the ideal assumption in the theoretical security proof of the CV-QKD protocol may be compromised in practical implementations, an eavesdropper can take advantage of security holes created by implementation imperfections to obtain critical information.
To improve performance, efforts are currently underway to develop parameter estimation, use photon subtraction, non-gaussian post-selection, discrete modulation, etc.; recently, the concept of optimizing communication strategies has also been proposed in non-gaussian noise channels. Even so, practical implementation remains a challenging problem, even for a single attack, still requiring extremely high efficiency homodyne detection. To date, the only experimentally proven continuous variable measurement device independent quantum key distribution system (Continuous Variable Measurement Device Independent Quantum Key Distribution, CV-MDI-QKD) is based on free space transport and advanced detection techniques with an efficiency of about 98%. In practice, fiber-based homodyne detection has an overall efficiency of about 60% at telecommunications wavelengths.
The existing continuous variable sub-key distribution method allows two remote authentication users (Alice and Bob) to establish a security key through an unreliable quantum channel and an authenticated classical channel by coherent detection, and the ideal implementation of the security key can be approximately close to the limit of the capacity of an unrepeatered quantum communication key, but the ideal assumption proposed at present has difficulty in implementation, such as that in the prior art CN201810512409.X, the key information is easily obtained by a third party eavesdropper by utilizing security holes generated by the imperfection of the security key.
Aiming at the actual security hole of a receiving party measuring end, a Gaussian-modulated coherent-state (GMCS) continuous variable measuring equipment independent quantum key distribution method is provided, so that the side channel attack can be effectively resisted, but the theoretical performance, key generation rate and safe transmission distance of the GMCS CV-MDI-QKD can be limited due to the induced high equivalent excessive noise; the concepts that are currently dedicated to the development of parameter estimation, the use of photon subtraction, the use of non-gaussian post-selection, and the optimization of communication strategies are proposed, however their practical implementation has difficulties, even though extremely high efficiency homodyne detection is still required for a single attack.
Disclosure of Invention
Aiming at the problems in the related art, the invention provides a CV-MDI-QKD system and a method based on DMPM, which are used for overcoming the technical problems existing in the prior art, and the key coding in the invention is based on specific phase selection of discrete distribution matching instead of directly coding information on orthogonal values of continuous distribution for further judgment, thereby effectively reducing the required detection efficiency and being beneficial to weakening the influence of excessive noise of channels on key rate.
The technical scheme of the invention is realized as follows: the CV-MDI-QKD system based on the DMPM comprises a user transmitting end and a user receiving end, wherein the user transmitting end and the user receiving end are connected through a public channel and a quantum channel;
The user transmitting end comprises n ALICE transmitters and n BOB transmitters, and n is a positive integer; wherein the n aluminum senders are a first aluminum sender aluminum 1, a second aluminum sender aluminum 2, … …, and an nth aluminum sender aluminum n, respectively; the n BOB senders are respectively a first BOB sender BOB1, a second BOB sender BOB2, a … … and an nth BOB sender BOB n; each ALICE sender and each BOB sender independently prepare a coherent state at the same time;
the user receiving end comprises a receiving party Charlie; the user transmitting end further comprises a first frequency stabilization laser L1 and a first beam splitter BS1 which are connected in sequence;
the first frequency stabilization laser L1 emits laser, the laser is divided into two light signals by the first beam splitter BS1, one light signal is sent to n ALICE senders to prepare first coherent state light signals, and the first coherent state light signals are sent to the receiving party Charlie through quantum channels; the other beam of optical signals are sent to n BOB senders to prepare second coherent optical signals, and the second coherent optical signals are sent to the receiving party Charlie through quantum channels; the first coherent optical signal and the second coherent optical signal interfere at the receiving party Charlie to obtain a first interference optical signal; the receiving party Charlie detects the quantum state of the first interference optical signal and publishes the measurement result in a public channel; the quantum states include the coherent states.
Further, the receiving party Charlie includes a first polarization controller PC1, a second polarization controller PC2 and a second beam splitter BS2; the first polarization controller PC1 and the second polarization controller PC2 are respectively connected with the second beam splitter BS2;
the first coherent optical signal is sent to the second beam splitter BS2 through the first polarization controller PC 1; the second coherent optical signal is sent to a second beam splitter BS2 through a second polarization controller PC 2; the first coherent optical signal and the second coherent optical signal interfere in the second beam splitter BS2 to obtain a first interference optical signal;
the first polarization controller PC1 and the second polarization controller PC2 are used for adjusting and keeping the polarization directions of the first coherent optical signal and the second coherent optical signal consistent.
Further, the user transmitting end further comprises a first wavelength division multiplexer DWDM1, a second wavelength division multiplexer DWDM2, a third wavelength division multiplexer DWDM3 and a fourth wavelength division multiplexer DWDM4;
n ALICE senders are connected with the first beam splitter BS1 through the first wavelength division multiplexer DWDM1, and n BOB senders are connected with the first beam splitter BS1 through the third wavelength division multiplexer DWDM 3;
the first polarization controller PC1 is connected with n ALICE senders through a second wavelength division multiplexer DWDM 2; the second polarization controller PC2 is connected with n BOB senders through a fourth wavelength division multiplexer DWDM4;
The second wavelength division multiplexer DWDM2 is connected with the input end of the first polarization controller PC1 through a quantum channel; the fourth wavelength division multiplexer DWDM4 is connected with the input end of the second polarization controller PC2 through a quantum channel;
the first coherent optical signal is sent to a first polarization controller PC1 through a second wavelength division multiplexer DWDM 2; the second coherent optical signal is transmitted via a fourth wavelength division multiplexer DWDM4 to a second polarization controller PC2.
Further, each ALICE sender includes a first intensity modulator MZM1, a first phase modulator PM1, and a first attenuator VOA1 sequentially connected in sequence; each BOB sender comprises a second intensity modulator MZM2, a second phase modulator PM2 and a second attenuator VOA2 which are sequentially connected in sequence;
the first intensity modulator MZM1 is connected with the first wavelength division multiplexer DWDM1 through a quantum channel, and the first attenuator VOA1 is connected with the second wavelength division multiplexer DWDM2 through a quantum channel; the second intensity modulator MZM2 is connected with a third wavelength division multiplexer DWDM3 through a quantum channel, and the second attenuator VOA2 is connected with a fourth wavelength division multiplexer DWDM4 through a quantum channel;
two light signals split by the first beam splitter BS1, wherein one light signal sequentially passes through a first intensity modulator MZM1 and a first phase modulator PM1 to prepare the first coherent state light signal, and the other light signal sequentially passes through a second intensity modulator MZM2 and a second phase modulator PM2 to prepare the second coherent state light signal;
The first attenuator VOA1 is configured to control the intensity of the first coherent optical signal; the second attenuator VOA2 is configured to control the intensity of the second coherent optical signal.
Further, the amplitudes of the first coherent optical signal and the second coherent optical signal both meet the independent same Gaussian distribution with the mean value of 0 and the variance of mu; the first coherent state optical signal and the second coherent state optical signal respectively pass through a first attenuator VOA1 and a second attenuator VOA2 to control the intensity of the coherent state optical signal; the coherent optical signals after passing through the attenuator comprise M continuous pilot signals and N continuous data signals which are cascaded; the pilot signal is used for preliminarily obtaining the frequency offset between the optical signal before passing through the attenuator and the local oscillation light L0 of the sender; the data signal is used for further obtaining frequency offset and phase drift caused by path length fluctuation;
the second wavelength division multiplexer DWDM2 passes the first coherent optical signal with a distance L AC Is sent to the first polarization controller PC1; the fourth wavelength division multiplexer DWDM4 passes the second coherent optical signal with a distance L BC Is sent to the second polarization controller PC2;
The quantum channels are connected by adopting Single Mode Fiber (SMF); the single-mode fiber SMF is adopted, so that the channel loss in the signal transmission process can be effectively reduced, and the independent change of the polarization state is ensured;
the single mode fiber SMF of the ALICE sender to the receiver Charlie is used as a quantum channel, and the single mode fiber SMF of the BOB sender to the receiver Charlie is used as a delay line to synchronize the signals of both ALICE sender and BOB sender.
Further, the receiving party Charlie further includes a third beam splitter BS3, a fourth beam splitter BS4, a fifth beam splitter BS5, a third attenuator VOA3, a third phase modulator PM3, a photo monitor detector PD, a first homodyne detector Hom1, a second homodyne detector Hom2, an oscilloscope OSC, a second frequency stabilizing laser L2, and a switch S;
the output end of the first polarization controller PC1 and the output end of the second polarization controller PC2 are connected in parallel to the input end of the second beam splitter BS 2; the second beam splitter BS2 further includes two output ends, one output end is connected to the switch S, and the other output end is connected to the fifth beam splitter BS5; the second frequency stabilization laser L2 is sequentially connected with the third attenuator VOA3, the fourth beam splitter BS4 and the third phase modulator PM3, and the third phase modulator PM3 and the second beam splitter BS2 are connected in parallel to the fifth beam splitter BS5; two output ends of the fifth beam splitter BS5 are connected with a second homodyne detector Hom 2;
The switch S is used for switching on the first port or the second port, when the switch S is toggled upwards, the second port is switched on, and at the moment, the second beam splitter BS2 is connected with the photodetector PD; the switch S is shifted downwards to switch on the first port, and the second beam splitter BS2 and the fourth beam splitter BS4 are connected in parallel to the third beam splitter BS3 at the moment; two output ends of the third beam splitter BS3 are connected with a first homodyne detector Hom 1; the photoelectric detector PD, the first homodyne detector Hom1 and the second homodyne detector Hom2 are connected in parallel and connected to the oscillograph OSC;
the first homodyne detector Hom1 and the second homodyne detector Hom2 are used for measuring orthogonal components of the optical signals input into the homodyne detectors, and the homodyne detectors are not modulated on the states of the optical signals, so that a random generator is omitted, and the system structure is simpler;
the oscillograph OSC is used for collecting output results of the photo detector PD, the first homodyne detector Hom1 and the second homodyne detector Hom 2.
Further, the first interference optical signal is split by the second beam splitter BS2, and one optical signal propagates toward the switch S; the other beam of optical signal propagates towards the direction of the fifth beam splitter BS5 and interferes with the optical signal from the third phase modulator PM3 at the fifth beam splitter BS5 to obtain a third interference optical signal; the third interference optical signal is split into two beams of optical signals through a fifth beam splitter BS5, and the two beams of optical signals are respectively input from different ports of a second homodyne detector Hom 2; the second homodyne detector Hom2 is used for detecting the quadrature phase component of the quantum state of the third interference optical signal.
Further, when the switch S turns on the first port, the switch S turns on with the third beam splitter BS3 to form a first path; when the switch S is connected with the second port, the switch S is connected with the photoelectric detector PD to form a second path;
for the optical signal propagating towards the direction of the switch S, when the switch S is connected with the second port, the optical signal enters the second path, and then the photoelectric detector PD directly monitors the interference output power of the optical signal to obtain a monitoring result; the monitoring result of the photodetector PD is used to reflect the phase drift of the two optical signals split by the first beam splitter BS1 after passing through the quantum channels of the n ALICE transmitters and the n BOB transmitters, respectively;
when the switch S is connected with the first port, an optical signal enters a first path; the optical signal on the first path and the optical signal from the second frequency stabilization laser L2 interfere at the third beam splitter BS3 to obtain a second interference optical signal, and the second interference optical signal then enters the first homodyne detector Hom1; the first homodyne detector Hom1 is configured to detect a quadrature amplitude component of a quantum state of the second interference optical signal.
Further, the lasers emitted by the second frequency stabilization laser L2 and the first frequency stabilization laser L1 are continuous single-frequency optical signals, and the central wavelength of the continuous single-frequency optical signals is 1542.38nm and the line width is 150kHz; the optical power of the laser emitted by the second frequency stabilization laser L2 and the first frequency stabilization laser L1 is controlled to be-40.3 to-39.7 dbm, so that the requirements of a theoretical protocol on modulation variance can be well met;
Setting a power meter behind the second frequency-stabilized laser L2, wherein the power meter is used for detecting the optical power of the second frequency-stabilized laser L2 before experimental measurement, removing the power meter and connecting a third attenuator VOA3 to control the optical power of laser to be 4.7-5.3 dbm after the power meter detects that the optical power is-40.3-39.7 dbm, and then carrying out subsequent experimental measurement; the continuous single-frequency optical signal emitted by the second frequency stabilization laser L2 is used as a local oscillation light LO of a sender, and the power meter is adopted to monitor and adjust the optical power of the local oscillation light LO in real time;
the local oscillation light LO is split by a fourth beam splitter BS4, and one beam of optical signal interferes with the optical signal of the first path at a third beam splitter BS3 to obtain a second interference optical signal; the other beam of light signal passes through a third phase modulator PM3The optical signal separated from the second beam splitter BS2 towards the fifth beam splitter BS5 interferes at the fifth beam splitter BS5 to obtain the third interference optical signal; finally, the quadrature amplitude component X of the second interference light signal is measured by the first homodyne detector Hom1 A The second homodyne detector Hom2 measures the quadrature phase component P of the third interference light signal B The method comprises the steps of carrying out a first treatment on the surface of the Wherein the quadrature amplitude component X A Comprising a leading section XP A2 And data segment XD A2 The method comprises the steps of carrying out a first treatment on the surface of the The quadrature-phase component P B Comprises a leading section PP B2 And data segment PD B2 ；
The interference optical signals that interfere at the second beam splitter BS2, the third beam splitter BS3, and the fifth beam splitter BS5, respectively, are all finally connected in parallel to the oscillograph OSC for display.
Further, the first intensity modulator MZM1 and the second intensity modulator MZM2 are Mach-Zehnder modulators; the beam splitting ratios of the first beam splitter BS1, the second beam splitter BS2, the third beam splitter BS3, the fourth beam splitter BS4 and the fifth beam splitter BS5 are all 50:50.
Since we use the continuous wave mode of the quantum signal, the bandwidth of the whole system is mainly dependent on the bandwidth of the homodyne detector; the frequency drift of the system mainly depends on phase noise caused by spontaneous emission of the frequency stabilized laser, and is less influenced by other external factors.
The CV-MDI-QKD method based on the DMPM is applied to the CV-MDI-QKD system based on the DMPM, and comprises the following steps of:
s1: the first frequency-stabilized laser L1 emits continuous single-frequency light and is used as optical signals for n ALICE transmitters and n BOB transmitters;
s2: each all sender and each BOB sender prepare 4 coherent states respectively Wherein k=0, 1, 2, 3; alpha>、|αe iπ >Forming an X group; />Forming a P group;
s3: each ALICE sender and each BOB sender randomly select a coherent state from an X base and a P base respectively, and carry out key coding on the X base and the P base by utilizing random binary numbers 0 and 1; the intensity of the randomly selected coherent state is respectively adjusted through a first attenuator VOA1 and a second attenuator VOA 2;
s4: the coherent state after the intensity adjustment is respectively sent to a first polarization controller PC1 and a second polarization controller PC2 of a receiving party Charlie, and then the coherent state is manually adjusted by using the first polarization controller PC1 and the second polarization controller PC2, so that the polarization of the coherent state respectively sent by each ALICE sender and each BOB sender is kept consistent and interference occurs at a second beam splitter BS2 to obtain a first interference light signal;
s5: the coherence state of the first interference light signal is measured by a first homodyne detector Hom1 for quadrature amplitude component X A Measuring quadrature phase component P by second homodyne detector Hom2 B The receiving party Charlie sends the measurement result { X of each homodyne detector A2 ，P B2 -disclosed in a common channel authenticated by identity;
s6: checking and calibrating the receiving party Charlie with the measuring bases of all the ALICE transmitters and all the BOB transmitters to obtain an original key;
S7: based on the obtained original secret key, each ALICE sender and each BOB sender, further parameter acquisition is carried out by combining the result published in the public channel by the receiver Charlie to extract a series of secret keys, and information coordination and privacy amplification are carried out by utilizing the public channel passing identity authentication, so that the whole process of quantum secret key distribution is finally realized.
Further, each ALICE sender and each BOB sender can optimize the threshold of amplitude and phase matching, and the key rate and the safe transmission distance are improved to the maximum extent.
Further, in step S3, the key code is |α>Andcorresponding to 0, |αe in binary coding iπ >And->Corresponding to code 1.
Further, in step S6, each ALICE sender and each BOB sender first publish the respective selected measurement base in the common channel, and then, according to the measurement result published by the receiver Charlie, each ALICE sender and each BOB sender record their corresponding random binary numbers respectively; each ALICE sender keeps the obtained binary character string unchanged, and each BOB sender performs bit inversion on the corresponding code state of the BOB sender when the corresponding code state is P base, so as to generate a new binary sequence; each ALICE sender, each BOB sender, then gets a shared binary original key.
Further, DMPM is known as Discrete-modulated phase-matching;
the key coding is based on specific phase selection of discrete distribution matching, rather than directly coding key information on orthogonal values of continuous distribution for further judgment, and the coding mode can effectively reduce the required detection efficiency (Required detection efficiency, RDE) and weaken the influence of excessive noise of channels on the key generation rate;
wherein the specific phase selection based on discrete distribution matching is: the key information is encoded into a plurality of discrete and matched specific stages (discrete values K=0, 1, 2 and 3 are selected, different values are selected to form a measuring base), and after the receiver Charlie publicly announces the detection result of the same difference, the correlation can be established between legal parties (all senders and BOB senders).
Compared with the prior art, the invention has the beneficial effects that:
(1) The key information is encoded into a plurality of discrete specific stages, the key encoding is selected based on the specific phase of discrete distribution matching, instead of directly encoding the information on the orthogonal values of continuous distribution for further judgment, the required detection efficiency (Required detection efficiency, RDE) is effectively reduced, and the influence of excessive noise of a channel on the key rate is weakened;
(2) Compared with the traditional GMCS CV-MDI-QKD scheme, under the ideal asymmetric condition, the invention can realize safe key distribution under the condition of low-efficiency detection at present, and can reach the quantum limit of discrete coding quantum state discrimination against typical and strong non-Gaussian individual attack; for the symmetric case, the method can optimize the amplitude and threshold to maximize the key generation rate and the safe transmission distance.
Drawings
FIG. 1 is a block diagram of the overall architecture of a DMPM-based CV-MDI-QKD system of the present invention;
FIG. 2 is a block diagram of the first ALICE sender ALICE1, first BOB sender BOB1, and receiver Charlie connection of a DMPM-based CV-MDI-QKD system of the present invention;
FIG. 3 is a schematic diagram of the structure of each ALICE sender of a DMPM-based CV-MDI-QKD system of the present invention;
FIG. 4 is a schematic diagram of the structure of each BOB sender of a DMPM-based CV-MDI-QKD system of the present invention;
fig. 5 is a schematic diagram of the structure of a receiver Charlie of a DMPM-based CV-MDI-QKD system of the invention;
FIG. 6 is a technical flow diagram of a DMPM-based CV-MDI-QKD method of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention.
As shown in fig. 1-5, the present embodiment provides a DMPM-based CV-MDI-QKD system, including a user transmitting end and a user receiving end, where the user transmitting end and the user receiving end are connected through a common channel and a quantum channel;
the user transmitting end comprises n ALICE transmitters and n BOB transmitters, and n is a positive integer; wherein the n aluminum senders are a first aluminum sender aluminum 1, a second aluminum sender aluminum 2, … …, and an nth aluminum sender aluminum n, respectively; the n BOB senders are respectively a first BOB sender BOB1, a second BOB sender BOB2, a … … and an nth BOB sender BOB n; each ALICE sender and each BOB sender independently prepare a coherent state at the same time;
The user receiving end comprises a receiving party Charlie; the user transmitting end further comprises a first frequency stabilization laser L1 and a first beam splitter BS1 which are connected in sequence;
the first frequency stabilization laser L1 emits laser, the laser is divided into two light signals by the first beam splitter BS1, one light signal is sent to n ALICE senders to prepare first coherent state light signals, and the first coherent state light signals are sent to the receiving party Charlie through quantum channels; the other beam of optical signals are sent to n BOB senders to prepare second coherent optical signals, and the second coherent optical signals are sent to the receiving party Charlie through quantum channels; the first coherent optical signal and the second coherent optical signal interfere at the receiving party Charlie to obtain a first interference optical signal; the receiving party Charlie detects the quantum state of the first interference optical signal and publishes the measurement result in a public channel; the quantum states include the coherent states.
Specifically, the receiving party Charlie includes a first polarization controller PC1, a second polarization controller PC2, and a second beam splitter BS2; the first polarization controller PC1 and the second polarization controller PC2 are respectively connected with the second beam splitter BS2;
The first coherent optical signal is sent to the second beam splitter BS2 through the first polarization controller PC 1; the second coherent optical signal is sent to a second beam splitter BS2 through a second polarization controller PC 2; the first coherent optical signal and the second coherent optical signal interfere in the second beam splitter BS2 to obtain a first interference optical signal;
the first polarization controller PC1 and the second polarization controller PC2 are used for adjusting and keeping the polarization directions of the first coherent optical signal and the second coherent optical signal consistent.
Specifically, the user transmitting end further comprises a first wavelength division multiplexer DWDM1, a second wavelength division multiplexer DWDM2, a third wavelength division multiplexer DWDM3 and a fourth wavelength division multiplexer DWDM4;
n ALICE senders are connected with the first beam splitter BS1 through the first wavelength division multiplexer DWDM1, and n BOB senders are connected with the first beam splitter BS1 through the third wavelength division multiplexer DWDM 3;
the first polarization controller PC1 is connected with n ALICE senders through a second wavelength division multiplexer DWDM 2; the second polarization controller PC2 is connected with n BOB senders through a fourth wavelength division multiplexer DWDM4;
the second wavelength division multiplexer DWDM2 is connected with the input end of the first polarization controller PC1 through a quantum channel; the fourth wavelength division multiplexer DWDM4 is connected with the input end of the second polarization controller PC2 through a quantum channel;
The first coherent optical signal is sent to a first polarization controller PC1 through a second wavelength division multiplexer DWDM 2; the second coherent optical signal is transmitted via a fourth wavelength division multiplexer DWDM4 to a second polarization controller PC2.
Specifically, each ALICE sender includes a first intensity modulator MZM1, a first phase modulator PM1, and a first attenuator VOA1 sequentially connected in sequence; each BOB sender comprises a second intensity modulator MZM2, a second phase modulator PM2 and a second attenuator VOA2 which are sequentially connected in sequence;
the first intensity modulator MZM1 is connected with the first wavelength division multiplexer DWDM1 through a quantum channel, and the first attenuator VOA1 is connected with the second wavelength division multiplexer DWDM2 through a quantum channel; the second intensity modulator MZM2 is connected with a third wavelength division multiplexer DWDM3 through a quantum channel, and the second attenuator VOA2 is connected with a fourth wavelength division multiplexer DWDM4 through a quantum channel;
two light signals split by the first beam splitter BS1, wherein one light signal sequentially passes through a first intensity modulator MZM1 and a first phase modulator PM1 to prepare the first coherent state light signal, and the other light signal sequentially passes through a second intensity modulator MZM2 and a second phase modulator PM2 to prepare the second coherent state light signal;
The first attenuator VOA1 is configured to control the intensity of the first coherent optical signal; the second attenuator VOA2 is configured to control the intensity of the second coherent optical signal.
In this embodiment, the amplitudes of the first coherent optical signal and the second coherent optical signal both satisfy independent same gaussian distributions with a mean value of 0 and a variance of μ; the first coherent state optical signal and the second coherent state optical signal respectively pass through a first attenuator VOA1 and a second attenuator VOA2 to control the intensity of the coherent state optical signal; the coherent optical signals after passing through the attenuator comprise M continuous pilot signals and N continuous data signals which are cascaded; the pilot signal is used for preliminarily obtaining the frequency offset between the optical signal before passing through the attenuator and the local oscillation light L0 of the sender; the data signal is used for further obtaining frequency offset and phase drift caused by path length fluctuation;
the second wavelength division multiplexer DWDM2 passes the first coherent optical signal with a distance L AC Is sent to the first polarization controller PC1; the fourth wavelength division multiplexer DWDM4 passes the second coherent optical signal with a distance L BC Is sent to the second polarization controller PC2;
The quantum channels are connected by adopting Single Mode Fiber (SMF); the single-mode fiber SMF is adopted, so that the channel loss in the signal transmission process can be effectively reduced, and the independent change of the polarization state is ensured;
the single mode fiber SMF of the ALICE sender to the receiver Charlie is used as a quantum channel, and the single mode fiber SMF of the BOB sender to the receiver Charlie is used as a delay line to synchronize the signals of both ALICE sender and BOB sender.
Specifically, the receiving party Charlie further includes a third beam splitter BS3, a fourth beam splitter BS4, a fifth beam splitter BS5, a third attenuator VOA3, a third phase modulator PM3, a photo monitor detector PD, a first homodyne detector Hom1, a second homodyne detector Hom2, an oscilloscope OSC, a second frequency stabilizing laser L2, and a switch S;
the output end of the first polarization controller PC1 and the output end of the second polarization controller PC2 are connected in parallel to the input end of the second beam splitter BS 2; the second beam splitter BS2 further includes two output ends, one output end is connected to the switch S, and the other output end is connected to the fifth beam splitter BS5; the second frequency stabilization laser L2 is sequentially connected with the third attenuator VOA3, the fourth beam splitter BS4 and the third phase modulator PM3, and the third phase modulator PM3 and the second beam splitter BS2 are connected in parallel to the fifth beam splitter BS5; two output ends of the fifth beam splitter BS5 are connected with a second homodyne detector Hom 2;
The switch S is used for switching on the first port or the second port, when the switch S is toggled upwards, the second port is switched on, and at the moment, the second beam splitter BS2 is connected with the photodetector PD; the switch S is shifted downwards to switch on the first port, and the second beam splitter BS2 and the fourth beam splitter BS4 are connected in parallel to the third beam splitter BS3 at the moment; two output ends of the third beam splitter BS3 are connected with a first homodyne detector Hom 1; the photoelectric detector PD, the first homodyne detector Hom1 and the second homodyne detector Hom2 are connected in parallel and connected to the oscillograph OSC;
the first homodyne detector Hom1 and the second homodyne detector Hom2 are used for measuring orthogonal components of the optical signals input into the homodyne detectors, and the homodyne detectors are not modulated on the states of the optical signals, so that a random generator is omitted, and the system structure is simpler;
the oscillograph OSC is used for collecting output results of the photo detector PD, the first homodyne detector Hom1 and the second homodyne detector Hom 2.
Specifically, the first interference optical signal is split by the second beam splitter BS2, and one optical signal propagates toward the switch S; the other beam of optical signal propagates towards the direction of the fifth beam splitter BS5 and interferes with the optical signal from the third phase modulator PM3 at the fifth beam splitter BS5 to obtain a third interference optical signal; the third interference optical signal is split into two beams of optical signals through a fifth beam splitter BS5, and the two beams of optical signals are respectively input from different ports of a second homodyne detector Hom 2; the second homodyne detector Hom2 is used for detecting the quadrature phase component of the quantum state of the third interference optical signal.
Specifically, when the switch S turns on the first port, the switch S turns on with the third beam splitter BS3 to form a first path; when the switch S is connected with the second port, the switch S is connected with the photoelectric detector PD to form a second path;
for the optical signal propagating towards the direction of the switch S, when the switch S is connected with the second port, the optical signal enters the second path, and then the photoelectric detector PD directly monitors the interference output power of the optical signal to obtain a monitoring result; the monitoring result of the photodetector PD is used to reflect the phase drift of the two optical signals split by the first beam splitter BS1 after passing through the quantum channels of the n ALICE transmitters and the n BOB transmitters, respectively;
when the switch S is connected with the first port, an optical signal enters a first path; the optical signal on the first path and the optical signal from the second frequency stabilization laser L2 interfere at the third beam splitter BS3 to obtain a second interference optical signal, and the second interference optical signal then enters the first homodyne detector Hom1; the first homodyne detector Hom1 is configured to detect a quadrature amplitude component of a quantum state of the second interference optical signal.
Specifically, the lasers emitted by the second frequency stabilization laser L2 and the first frequency stabilization laser L1 are continuous single-frequency optical signals, and the central wavelength of the continuous single-frequency optical signals is 1542.38nm and the line width is 150kHz; the optical power of the laser emitted by the second frequency stabilization laser L2 and the first frequency stabilization laser L1 is controlled to be-40.3 to-39.7 dbm, so that the requirements of a theoretical protocol on modulation variance can be well met;
Specifically, in this embodiment, the optical power of the laser light emitted by the second frequency-stabilized laser L2 and the first frequency-stabilized laser L1 are controlled to be-40 dbm preferentially;
setting a power meter behind the second frequency-stabilized laser L2, wherein the power meter is used for detecting the optical power of the second frequency-stabilized laser L2 before experimental measurement, removing the power meter and connecting a third attenuator VOA3 to control the optical power of laser to be 4.7-5.3 dbm after the power meter detects that the optical power is-40.3-39.7 dbm, and then carrying out subsequent experimental measurement; the continuous single-frequency optical signal emitted by the second frequency stabilization laser L2 is used as a local oscillation light LO of a sender, and the power meter is adopted to monitor and adjust the optical power of the local oscillation light LO in real time;
specifically, in this embodiment, the second frequency stabilizing laser L2 preferably controls the optical power of the laser to 5dbm after removing the power meter and connecting the third attenuator VOA 3;
the local oscillation light LO is split by a fourth beam splitter BS4, and one beam of optical signal interferes with the optical signal of the first path at a third beam splitter BS3 to obtain a second interference optical signal; the other beam of optical signal is interfered at the fifth beam splitter BS5 by the optical signal separated from the second beam splitter BS2 in the direction of the fifth beam splitter BS5 through the third phase modulator PM3, so as to obtain the third interference optical signal; finally, the quadrature amplitude component X of the second interference light signal is measured by the first homodyne detector Hom1 A The second homodyne detector Hom2 measures the quadrature phase component P of the third interference light signal B The method comprises the steps of carrying out a first treatment on the surface of the Wherein the quadrature amplitude component X A Comprising a leading section XP A2 And data segment XD A2 The method comprises the steps of carrying out a first treatment on the surface of the The quadrature-phase component P B Comprises a leading section PP B2 And data segment PD B2 ；
The interference optical signals that interfere at the second beam splitter BS2, the third beam splitter BS3, and the fifth beam splitter BS5, respectively, are all finally connected in parallel to the oscillograph OSC for display.
Specifically, the first intensity modulator MZM1 and the second intensity modulator MZM2 are Mach-Zehnder modulators; the beam splitting ratios of the first beam splitter BS1, the second beam splitter BS2, the third beam splitter BS3, the fourth beam splitter BS4 and the fifth beam splitter BS5 are all 50:50.
Since we use the continuous wave mode of the quantum signal, the bandwidth of the whole system is mainly dependent on the bandwidth of the homodyne detector; the frequency drift of the system mainly depends on phase noise caused by spontaneous emission of the frequency stabilized laser, and is less influenced by other external factors.
As shown in fig. 6, the present embodiment further provides a DMPM-based CV-MDI-QKD method, which is applied to the above-mentioned DMPM-based CV-MDI-QKD system, and includes the following steps:
S1: the first frequency-stabilized laser L1 emits continuous single-frequency light and is used as optical signals for n ALICE transmitters and n BOB transmitters;
s2: each all sender and each BOB sender prepare 4 coherent states respectivelyWherein k=0, 1, 2, 3; alpha>、|αe iπ >Forming an X group; />Forming a P group;
s3: each ALICE sender and each BOB sender randomly select a coherent state from an X base and a P base respectively, and carry out key coding on the X base and the P base by utilizing random binary numbers 0 and 1; the intensity of the randomly selected coherent state is respectively adjusted through a first attenuator VOA1 and a second attenuator VOA 2;
s4: the coherent state after the intensity adjustment is respectively sent to a first polarization controller PC1 and a second polarization controller PC2 of a receiving party Charlie, and then the coherent state is manually adjusted by using the first polarization controller PC1 and the second polarization controller PC2, so that the polarization of the coherent state respectively sent by each ALICE sender and each BOB sender is kept consistent and interference occurs at a second beam splitter BS2 to obtain a first interference light signal;
s5: coherent state passing of first interference optical signalFirst homodyne detector Hom1 measures quadrature amplitude component X A Measuring quadrature phase component P by second homodyne detector Hom2 B The receiving party Charlie sends the measurement result { X of each homodyne detector A2 ，P B2 -disclosed in a common channel authenticated by identity;
s6: checking and calibrating the receiving party Charlie with the measuring bases of all the ALICE transmitters and all the BOB transmitters to obtain an original key;
s7: based on the obtained original secret key, each ALICE sender and each BOB sender, further parameter acquisition is carried out by combining the result published in the public channel by the receiver Charlie to extract a series of secret keys, and information coordination and privacy amplification are carried out by utilizing the public channel passing identity authentication, so that the whole process of quantum secret key distribution is finally realized.
Specifically, each ALICE sender and each BOB sender can optimize the threshold of amplitude and phase matching, and the key rate and the safe transmission distance are improved to the maximum extent.
Specifically, in step S3, the key code is |α>Andcorresponding to 0, |αe in binary coding iπ >And->Corresponding to code 1.
Specifically, in step S6, each ALICE sender and each BOB sender first publish the respective selected measurement base in the common channel, and then, according to the measurement result published by the receiver Charlie, each ALICE sender and each BOB sender record their corresponding random binary numbers respectively; each ALICE sender keeps the obtained binary character string unchanged, and each BOB sender performs bit inversion on the corresponding code state of the BOB sender when the corresponding code state is P base, so as to generate a new binary sequence; each ALICE sender, each BOB sender, then gets a shared binary original key.
Specifically, DMPM is known as Discrete-modulated phase-matching, i.e., discrete modulation phase matching;
the key coding is based on specific phase selection of discrete distribution matching, rather than directly coding key information on orthogonal values of continuous distribution for further judgment, and the coding mode can effectively reduce the required detection efficiency (Required detection efficiency, RDE) and weaken the influence of excessive noise of channels on the key generation rate;
wherein the specific phase selection based on discrete distribution matching is: the key information is encoded into a plurality of discrete and matched specific stages (discrete values K=0, 1, 2 and 3 are selected, different values are selected to form a measuring base), and after the receiver Charlie publicly announces the detection result of the same difference, the correlation can be established between legal parties (all senders and BOB senders).
Variations and modifications to the above would be obvious to persons skilled in the art to which the invention pertains from the foregoing description and teachings. Therefore, the invention is not limited to the specific embodiments disclosed and described above, but some modifications and changes of the invention should be also included in the scope of the claims of the invention. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not limit the present invention in any way.
Claims (10)
1. The CV-MDI-QKD system based on the DMPM comprises a user transmitting end and a user receiving end, wherein the user transmitting end and the user receiving end are connected through a public channel and a quantum channel; it is characterized in that the method comprises the steps of,
the user transmitting end comprises n ALICE transmitters and n BOB transmitters, and n is a positive integer; wherein the n aluminum senders are a first aluminum sender aluminum 1, a second aluminum sender aluminum 2, … …, and an nth aluminum sender aluminum n, respectively; the n BOB senders are respectively a first BOB sender BOB1, a second BOB sender BOB2, a … … and an nth BOB sender BOB n; each ALICE sender and each BOB sender independently prepare a coherent state at the same time;
the user transmitting end further comprises a first frequency stabilization laser L1 and a first beam splitter BS1 which are connected in sequence;
the user receiving end comprises a receiving party Charlie;
the first frequency stabilization laser L1 emits laser, the laser is divided into two light signals by the first beam splitter BS1, one light signal is sent to n ALICE senders to prepare first coherent state light signals, and the first coherent state light signals are sent to the receiving party Charlie through quantum channels;
the other beam of optical signals are sent to n BOB senders to prepare second coherent optical signals, and the second coherent optical signals are sent to the receiving party Charlie through quantum channels;
The first coherent optical signal and the second coherent optical signal interfere at the receiving party Charlie to obtain a first interference optical signal; the receiving party Charlie detects the quantum state of the first interference optical signal and publishes the measurement result in a public channel; the quantum states include the coherent states.
2. The DMPM-based CV-MDI-QKD system of claim 1, wherein the receiver Charlie includes a first polarization controller PC1, a second polarization controller PC2, and a second beam splitter BS2; the first polarization controller PC1 and the second polarization controller PC2 are respectively connected with the second beam splitter BS2;
the first coherent optical signal is sent to the second beam splitter BS2 through the first polarization controller PC 1; the second coherent optical signal is sent to a second beam splitter BS2 through a second polarization controller PC 2; the first coherent optical signal and the second coherent optical signal interfere in the second beam splitter BS2 to obtain a first interference optical signal;
the first polarization controller PC1 and the second polarization controller PC2 are used for adjusting and keeping the polarization directions of the first coherent optical signal and the second coherent optical signal consistent.
3. The DMPM-based CV-MDI-QKD system of claim 2, wherein said user transmitter further includes a first wavelength division multiplexer DWDM1, a second wavelength division multiplexer DWDM2, a third wavelength division multiplexer DWDM3, and a fourth wavelength division multiplexer DWDM4;
n ALICE senders are connected with the first beam splitter BS1 through the first wavelength division multiplexer DWDM1, and n BOB senders are connected with the first beam splitter BS1 through the third wavelength division multiplexer DWDM 3;
the first polarization controller PC1 is connected with n ALICE senders through a second wavelength division multiplexer DWDM 2; the second polarization controller PC2 is connected with n BOB senders through a fourth wavelength division multiplexer DWDM 4;
the second wavelength division multiplexer DWDM2 is connected with the input end of the first polarization controller PC1 through a quantum channel; the fourth wavelength division multiplexer DWDM4 is connected with the input end of the second polarization controller PC2 through a quantum channel;
the first coherent optical signal is sent to a first polarization controller PC1 through a second wavelength division multiplexer DWDM 2; the second coherent optical signal is transmitted via a fourth wavelength division multiplexer DWDM4 to a second polarization controller PC2.
4. A DMPM-based CV-MDI-QKD system according to claim 3, wherein each of said all senders includes a first intensity modulator MZM1, a first phase modulator PM1, and a first attenuator VOA1 connected in sequence; each BOB sender comprises a second intensity modulator MZM2, a second phase modulator PM2 and a second attenuator VOA2 which are sequentially connected in sequence;
The first intensity modulator MZM1 is connected with the first wavelength division multiplexer DWDM1 through a quantum channel, and the first attenuator VOA1 is connected with the second wavelength division multiplexer DWDM2 through a quantum channel; the second intensity modulator MZM2 is connected with a third wavelength division multiplexer DWDM3 through a quantum channel, and the second attenuator VOA2 is connected with a fourth wavelength division multiplexer DWDM4 through a quantum channel;
two light signals split by the first beam splitter BS1, wherein one light signal sequentially passes through a first intensity modulator MZM1 and a first phase modulator PM1 to prepare the first coherent state light signal, and the other light signal sequentially passes through a second intensity modulator MZM2 and a second phase modulator PM2 to prepare the second coherent state light signal;
the first attenuator VOA1 is configured to control the intensity of the first coherent optical signal; the second attenuator VOA2 is configured to control the intensity of the second coherent optical signal.
5. The DMPM-based CV-MDI-QKD system of claim 4, wherein the first coherent optical signal and the second coherent optical signal each have an amplitude that satisfies an independent same gaussian distribution with a mean of 0 and a variance μ; the first coherent state optical signal and the second coherent state optical signal respectively pass through a first attenuator VOA1 and a second attenuator VOA2 to control the intensity of the coherent state optical signal; the coherent optical signals after passing through the attenuator comprise M continuous pilot signals and N continuous data signals which are cascaded;
The second wavelength division multiplexer DWDM2 passes the first coherent optical signal with a distance L AC Is sent to the first polarization controller PC1; the fourth wavelength division multiplexer DWDM4 passes the second coherent optical signal with a distance L BC Is sent to the second polarization controller PC2;
the quantum channels are connected by adopting Single Mode Fiber (SMF); and taking a single-mode fiber SMF from an ALICE sender to a Charlie receiver as a quantum channel.
6. The DMPM-based CV-MDI-QKD system of claim 5, wherein the receiver Charlie further comprises a third beam splitter BS3, a fourth beam splitter BS4, a fifth beam splitter BS5, a third attenuator VOA3, a third phase modulator PM3, a photo-monitor detector PD, a first homodyne detector Hom1, a second homodyne detector Hom2, an oscilloscope OSC, a second frequency stabilizing laser L2, and a switch S;
the output end of the first polarization controller PC1 and the output end of the second polarization controller PC2 are connected in parallel to the input end of the second beam splitter BS 2; the second beam splitter BS2 further includes two output ends, one output end is connected to the switch S, and the other output end is connected to the fifth beam splitter BS5; the second frequency stabilization laser L2 is sequentially connected with the third attenuator VOA3, the fourth beam splitter BS4 and the third phase modulator PM3, and the third phase modulator PM3 and the second beam splitter BS2 are connected in parallel to the fifth beam splitter BS5; two output ends of the fifth beam splitter BS5 are connected with a second homodyne detector Hom 2;
The switch S is used for switching on the first port or the second port, when the switch S is toggled upwards, the second port is switched on, and at the moment, the second beam splitter BS2 is connected with the photodetector PD; the switch S is shifted downwards to switch on the first port, and the second beam splitter BS2 and the fourth beam splitter BS4 are connected in parallel to the third beam splitter BS3 at the moment; two output ends of the third beam splitter BS3 are connected with a first homodyne detector Hom 1; the photoelectric detector PD, the first homodyne detector Hom1 and the second homodyne detector Hom2 are connected in parallel and connected to the oscillograph OSC;
the first homodyne detector Hom1 and the second homodyne detector Hom2 are used for measuring orthogonal components of the optical signals input into the homodyne detector;
the oscillograph OSC is used for collecting output results of the photo detector PD, the first homodyne detector Hom1 and the second homodyne detector Hom 2.
7. The DMPM-based CV-MDI-QKD system of claim 6, wherein the first interfering optical signal is split by a second beam splitter BS2, and a beam of optical signal propagates in the direction of switch S; the other beam of optical signal propagates towards the direction of the fifth beam splitter BS5 and interferes with the optical signal from the third phase modulator PM3 at the fifth beam splitter BS5 to obtain a third interference optical signal; the third interference optical signal is split into two beams of optical signals through a fifth beam splitter BS5, and the two beams of optical signals are respectively input from different ports of a second homodyne detector Hom 2; the second homodyne detector Hom2 is used for detecting the quadrature phase component of the quantum state of the third interference optical signal;
When the switch S is connected with the first port, the switch S is connected with the third beam splitter BS3 to form a first path; when the switch S is connected with the second port, the switch S is connected with the photoelectric detector PD to form a second path;
for the optical signal propagating towards the direction of the switch S, when the switch S is connected with the second port, the optical signal enters the second path, and then the photoelectric detector PD directly monitors the interference output power of the optical signal to obtain a monitoring result; the monitoring result of the photodetector PD is used to reflect the phase drift of the two optical signals split by the first beam splitter BS1 after passing through the quantum channels of the n ALICE transmitters and the n BOB transmitters, respectively;
when the switch S is connected with the first port, an optical signal enters a first path; the optical signal on the first path and the optical signal from the second frequency stabilization laser L2 interfere at the third beam splitter BS3 to obtain a second interference optical signal, and the second interference optical signal then enters the first homodyne detector Hom1; the first homodyne detector Hom1 is configured to detect a quadrature amplitude component of a quantum state of the second interference optical signal.
8. The DMPM-based CV-MDI-QKD system of claim 7, wherein the laser light emitted by the second frequency-stabilized laser L2 and the laser light emitted by the first frequency-stabilized laser L1 are continuous single-frequency optical signals, and the optical power of the laser light emitted by the second frequency-stabilized laser L2 and the laser light emitted by the first frequency-stabilized laser L1 are controlled to be-40.3 dbm to-39.7 dbm;
Setting a power meter behind the second frequency-stabilized laser L2, wherein the power meter is used for detecting the optical power of the second frequency-stabilized laser L2 before experimental measurement, removing the power meter and connecting a third attenuator VOA3 to control the optical power of laser to be 4.7-5.3 dbm after the power meter detects that the optical power is-40.3-39.7 dbm, and then carrying out subsequent experimental measurement; the continuous single-frequency optical signal emitted by the second frequency stabilization laser L2 is used as a local oscillation light LO of a sender, and the power meter is adopted to monitor and adjust the optical power of the local oscillation light LO in real time;
the local oscillation light LO is split by a fourth beam splitter BS4, and one beam of optical signal interferes with the optical signal of the first path at a third beam splitter BS3 to obtain a second interference optical signal; the other beam of optical signal is interfered at the fifth beam splitter BS5 by the optical signal separated from the second beam splitter BS2 in the direction of the fifth beam splitter BS5 through the third phase modulator PM3, so as to obtain the third interference optical signal; finally, the process is carried out,measuring the quadrature amplitude component X of the second interference light signal by the first homodyne detector Hom1 A The second homodyne detector Hom2 measures the quadrature phase component P of the third interference light signal B The method comprises the steps of carrying out a first treatment on the surface of the Wherein the quadrature amplitude component X A Comprising a leading section XP A2 And data segment XD A2 The method comprises the steps of carrying out a first treatment on the surface of the The quadrature-phase component P B Comprises a leading section PP B2 And data segment PD B2 ；
The interference optical signals respectively interfered at the second beam splitter BS2, the third beam splitter BS3 and the fifth beam splitter BS5 are finally connected in parallel to the oscillograph OSC for displaying;
the first intensity modulator MZM1 and the second intensity modulator MZM2 are Mach-Zehnder modulators; the beam splitting ratios of the first beam splitter BS1, the second beam splitter BS2, the third beam splitter BS3, the fourth beam splitter BS4 and the fifth beam splitter BS5 are all 50:50.
9. A DMPM-based CV-MDI-QKD method, applied to a DMPM-based CV-MDI-QKD system according to any one of claims 1 to 8, comprising the steps of:
s1: the first frequency-stabilized laser L1 emits continuous single-frequency light and is used as optical signals for n ALICE transmitters and n BOB transmitters;
s2: each all sender and each BOB sender prepare 4 coherent states respectivelyWherein k=0, 1, 2, 3; alpha>、|αe iπ >Forming an X group; />Forming a P group;
s3: each ALICE sender and each BOB sender randomly select a coherent state from an X base and a P base respectively, and carry out key coding on the X base and the P base by utilizing random binary numbers 0 and 1; the intensity of the randomly selected coherent state is respectively adjusted through a first attenuator VOA1 and a second attenuator VOA 2;
S4: the coherent state after the intensity adjustment is respectively sent to a first polarization controller PC1 and a second polarization controller PC2 of a receiving party Charlie, and then the coherent state is manually adjusted by using the first polarization controller PC1 and the second polarization controller PC2, so that the polarization of the coherent state respectively sent by each ALICE sender and each BOB sender is kept consistent and interference occurs at a second beam splitter BS2 to obtain a first interference light signal;
s5: the coherence state of the first interference light signal is measured by a first homodyne detector Hom1 for quadrature amplitude component X A Measuring quadrature phase component P by second homodyne detector Hom2 B The receiving party Charlie sends the measurement result { X of each homodyne detector A2 ，P B2 -disclosed in a common channel authenticated by identity;
s6: checking and calibrating the receiving party Charlie with the measuring bases of all the ALICE transmitters and all the BOB transmitters to obtain an original key;
s7: based on the obtained original secret key, each ALICE sender and each BOB sender, further parameter acquisition is carried out by combining the result published in the public channel by the receiver Charlie to extract a series of secret keys, and information coordination and privacy amplification are carried out by utilizing the public channel passing identity authentication, so that the whole process of quantum secret key distribution is finally realized.
10. The DMPM-based CV-MDI-QKD method according to claim 9, wherein in step S3, the key code is |α>Andcorresponding to 0, |αe in binary coding iπ >And->Corresponding to code 1;
the key encoding is based on a particular phase selection of discrete distribution matches;
in step S6, each ALICE sender and each BOB sender first publish the measurement base selected by each in the common channel, and then record the corresponding random binary numbers according to the measurement result published by the receiver Charlie; each ALICE sender keeps the obtained binary character string unchanged, and each BOB sender performs bit inversion on the corresponding code state of the BOB sender when the corresponding code state is P base, so as to generate a new binary sequence; each ALICE sender, each BOB sender, then gets a shared binary original key.
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